30 Seconds 10 Time’s Up! 3 Minutes 1 Minute 4 Minutes 1 2 5 2 Minutes Bellringer Mon, 12/7 What is mitosis? What are the phases of mitosis again? How many cells do we get after mitosis? Quickly draw a chromosome! Look up and tell me what is meiosis! Use your books! 5 MINS today! REMINDERS: HW #14 due Fri, Progress Reports Grades this Wed,LAB FEE anytime!!! 30 Seconds 10 Time’s Up! 3 Minutes 1 Minute 4 Minutes 1 2 5 2 Minutes 8 9 7 6 4 3

Meiosis

Reminders, Review and Something New Chromosomes = condensed chromatin (DNA) Made up of 2 sister chromatids held together in by the centromere Genes- sections of a chromosome responsible for one trait (eye color, height, etc)

Again, how many chromosomes do we have? Meiosis Again, how many chromosomes do we have? 23 (Maternal) + 23 (Paternal)= Total 46 1/16/2019 G. Podgorski, Biology 1010 4

What is MEIOSIS? Cell division that results in 4 daughter cells with half as many chromosomes as the parent cells!

Meiosis Parent cell – chromosome pair Chromosomes copied 1st division - pairs split 2nd division – produces 4 gamete cells with ½ the original no. of chromosomes

What cells go through meiosis? • only gametes or sex cells…. And we get… males-sperm and females-eggs

Why 1/2 the chromosomes in gametes? Why do we need meiosis? To reduce the number of chromosomes in 1/2 in gametes (sex cells)! Why 1/2 the chromosomes in gametes? the male and female gametes need to provide ½ the chromosomes each – so the offspring has one complete set (1/2 from mom and 1/2 from dad)!

Meiosis – PMAT I and II Parent cell Meiosis I First division Meiosis II Second division 4 daughter cells

Metaphase I: homologous chromosomes align in the middle of the cell! Meiosis 1/16/2019 Meiosis I Prophase I: homologous pairs (and copies) synapse (pair up). Crossing over occurs! Metaphase I: homologous chromosomes align in the middle of the cell! G. Podgorski, Biology 1010

What are homologous chromosomes? paired chromosomes with genes for the same trait aligned

Anaphase I: homologous chromosomes move to opposite ends Telophase I: 2 nuclei form, original cell finishes to divide

Meiosis II No INTERPHASE or DNA copied between I and II Prophase II: chromosomes condense again and start to move toward the center Metaphase II chromosomes line up in the center of cells

Anaphase II: sister chromatids separate to opposite poles Telophase II: two nuclei form for each of the cells Cytokinesis happens like in mitosis! 4 daughter cells with half the amount of chromosomes formed!

Results after meiosis… 4 Sex cells (gametes) that are haploid (n) - half as many chromosomes as parent cell (2n)

n = number of chromosomes from each parent Meiosis 1/16/2019 n n = number of chromosomes from each parent Gametes (sex cells)- haploid 2n Body cells diploid G. Podgorski, Biology 1010

Diploid vs. Haploid Organism Gamete (n) Body Cell (2n) Humans 23 46 Mosquito 3 6 Toad 11 22 Potato 24 48 Dog 39 78

Stages of Meiosis Meiosis I and Meiosis II

Meiosis 1/16/2019 G. Podgorski, Biology 1010

What next? Fertilization Meiosis 1/16/2019 What next? Fertilization Egg (n) + Sperm (n) = Zygote (2n) G. Podgorski, Biology 1010

Zygote>Embryo>Fetus A fertilized egg with diploid set of chromosomes. After fertilization, the zygote divides by mitosis and becomes an embryo. Later, the embryo becomes a fetus

Mitosis vs. Meiosis

2 Key Differences Between Mitosis and Meiosis 1/16/2019 2 Key Differences Between Mitosis and Meiosis 1. Look at the Way Chromosomes Pair and Align Meiosis Mitosis G. Podgorski, Biology 1010

Chromosomes exchange genetic material between homologous pairs! Meiosis 1/16/2019 2. Crossing-Over Chromosomes exchange genetic material between homologous pairs! G. Podgorski, Biology 1010